Test heads of this kind are known for testing electric and electronic circuits, especially for testing wafers. For electrical testing, test contact pins of the test head are brought into physical contact with corresponding electric surface contacts of the test specimen, e.g. by raising the test specimen by means of a lifting device and, in the process, pressing it against the ends of the test contact pins. During the contacting of the test specimen, the other ends of the test contact pins come up against surface contacts of a contact clearance enlargement device which serves to increase the contact clearance. In this context, it should be noted that the surface contacts of the wafer are within a very restricted area, and therefore the test contact pins, which are, in particular, designed as buckling beams, have only minimal contact clearances with respect to one another. By means of the contact clearance enlargement device, the contact clearances can be increased to such an extent that it is possible, by means of connection leads, to connect a testing device which switches test paths during electrical testing in order to test the test specimen for electric functioning capacity. The test contact pins are held by means of guide plates, wherein at least two guide plates are arranged spaced apart and have guide holes through which the test contact pins pass. The guide plates are made of an electrically nonconductive material, e.g. ceramics. The test contact pins are composed of a material of very good electrical conductivity which simultaneously has a certain elasticity to enable the test contact pins to bend sideways slightly during physical contact. In order to position the at least two guide plates relative to one another and to keep them apart, a spacer is provided, said spacer being formed by a plurality of cross-struts extending over the entire length of the plates and arranged spaced apart and adjacent to one another. These cross-struts take up a relatively large amount of space, which is not available as a test surface since it is not possible to arrange any test contact pins there. Moreover, there is the disadvantage that contact accuracy is not always assured owing to the effect of temperature, since a kind of bimetallic effect arises, leading possibly to distortions, i.e. the test contact pins come to rest inaccurately or not at all on the surface contacts of the test specimen which are to be contacted and/or on those of the contact clearance enlargement device, with the result that incorrect measurements are performed. The effect of temperature is evident particularly when the test specimen is exposed to different test temperatures during electrical testing in order to test its functioning capacity in a temperature range. The temperature range can extend from double-digit minus temperatures to triple-digit plus temperatures.
It is therefore the underlying object of the invention to specify a test head of the type stated at the outset which ensures highly accurate contacting which is maintained even at different temperatures, while furthermore an enlarged test area is available.